The present invention relates generally to cooktops, and more particularly, to a controller and methods of operating a radiant electric heater unit for cooktops.
Radiant electric heating units, as is well-known in the art, comprise an electrical heating element such as a coil heating element, or a ribbon heating element. In conventional heating units, the ends of the heating element connect through a thermal switch or limiter to an electrical circuit by which current is supplied to the heating element. The unit is installed beneath a cooking surface upon which utensils are placed. When a utensil is placed on the top of the cooking surface, the utensil is heated by direct radiant energy passing through the cooking surface. The utensil is also partially heated by conduction through absorbed radiant energy in the cooking surface. The thermal switch is responsive to the heating unit temperature exceeding a preset temperature to open the circuit path between a power source and the heating element to cut off current flow to the heating element. When the temperature falls back below the preset temperature, the switch reconnects the circuit path to restore the current flow to the heating element.
There are a number of problems with these heating units. One of these is the thermal switch. The thermal switch is expensive, representing 20-30% of the total cost of a heating unit. The switch assembly is a primary source of heating unit failure. It is simply too expensive to replace a failed switch. Rather, when the switch fails, the heating unit is discarded and a new heating unit is substituted in its place. Elimination of the existing thermal switch would not only be a substantial cost savings, but would also improve the service life of a heating unit; provided, that proper temperature control of the heating unit is still maintained. Moreover, these heating units are installed beneath a sheet of glass-ceramic material. This makes removal and installation difficult if the heating unit fails.
There is also a need for boiling liquids faster. Typical heating units drive the temperature to a particular set point without regard to the type of utensil that is on the heating unit or its location. The type of utensil and its location on the heating unit can affect system performance and the time to boil liquids. For example, a concave utensil reflects radiant energy back into the heating unit. A xe2x80x9chot spotxe2x80x9d may be formed in the glass-ceramic material underneath the concave portion of the utensil. The pocket of air under the concave portion of the utensil will serve as an insulator, preventing the spot from cooling. Moreover, an off-center utensil can cause portions of the glass-ceramic material not covered by the utensil to reach excessive temperatures. Without knowing the type of utensil or its location on the heating unit, these extreme conditions must be considered when determining the maximum temperature set point in the heating unit. This may result in a lower maximum set point for all types of utensils. A lower maximum set point, however, increases the time to boil liquids in flat pans that are centered correctly. Thus, a further need exists for a controller and methods of determining the type of utensil and whether it was centered properly. The controller could then dynamically change the temperature set point to optimally boil liquids.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
To that end, the present invention includes a controller for a heating unit. The heating unit is capable of generating heat to a utensil and has a temperature sensor, a heating element, and a cooking surface. The controller has a means for measuring a temperature of a cavity within the heating unit, a means for controlling the application of power to the heating element, and a means for determining whether to control the application of power to the heating element in an overdrive state based on a type of utensil that is located on the heating unit.
The means for measuring the temperature of the cavity may include the receiving of a signal generated from the temperature sensor. The means for controlling the application of power to the heating element may include the generation of a duty cycle signal to a power source that is electrically connected to the heating element. The means for determining whether to control the application of power to the heating element in an overdrive state may include a measurement of a temperature profile of the cavity temperature.
In another embodiment, the present invention includes temperature control system for a heating unit in a cooktop. The heating unit has a heating element disposed below a cooking surface and is capable of generating heat to a utensil located on the cooking surface. The temperature control system includes a temperature sensor and a controller. The temperature sensor measures the temperature within a cavity of the heating unit. The controller is capable of receiving a signal from the temperature sensor reflecting the measured temperature within the cavity and controlling the application of power to the heating element. The controller is further capable of determining the type of utensil that is located on the heating unit and is capable of controlling the application of power to the heating element in an overdrive state based on the type of utensil that is located on the heating unit.
The temperature control system may further include a power source and a user control knob. The power source is electrically connected to the heating element and electrically connected to the controller. The user control knob enables the user to select a temperature setting. The controller may further have a means for measuring the temperature profile of the cavity. This may include a means for measuring a first period of time that it takes the measured temperature of the cavity to travel from a first temperature to a second temperature. It may also include a means for measuring a second period of time that it takes the measured temperature of the cavity to travel from a third temperature to a fourth temperature.
In a further embodiment, the present invention includes a method of operating a heating unit at a first temperature setting. The heating unit has a heater element that radiates infrared energy and a temperature sensor adapted to measuring a sensed temperature in the heating unit. The method includes the steps of: measuring a first period of time from a first temperature to a second temperature; measuring a second period of time from a third temperature to a fourth temperature; comparing the first period of time to the second period of time; determining whether to increase the first temperature setting to a second temperature setting in the heating unit; and increasing the first temperature setting to a second temperature setting if it is determined that the first temperature setting may be increased from the first temperature to the second temperature.
The method may be performed by a controller in the cooktop. The controller is capable of receiving the sensed temperature from the temperature sensor. The controller is also electrically connected to the heater element to maintain the first and second temperature settings. In one embodiment, the second temperature setting is greater than the first temperature setting. Moreover, the determining step may further include the step of determining whether a utensil on the heating unit is concave.
Another embodiment of the present invention includes another method of operating a heating unit at a first temperature setting. However, this method includes the steps of: measuring a first increase in the sensed temperature during a first period of time; measuring a second increase in the sensed temperature during a second period of time; comparing the first increase in the sensed temperature to the second increase in sensed temperature; determining whether to increase the first temperature setting to a second temperature setting in the heating unit; and increasing the first temperature setting to the second temperature setting if it is determined that the first temperature setting may be increased from the first temperature setting to the second temperature setting.
The above summary of the present invention is not intended to represent each embodiment, or every aspect of the present invention. This is the purpose of the figures and detailed description that follows.